Related Publications

Pathogen

Septoria leaf spot is caused by the fungus Septoria lycopersici. The disease is particularly destructive in seasons of moderate temperature and abundant rainfall, with the ability to reduce tomato yields dramatically.

Identification

Circular, tan to gray, lesions develop on the lower leaves and stems of the plant. Lesions are typically small (<1/8 in), but as lesions become more numerous the entire leaf may become blighted. The lesions generally have a dark-brown perimeter and a yellow halo may develop around the leaf lesions. Small dark spots may appear in the center of the lesion – these are pycnidia, the fruiting body of the fungus where spores are produced. On the underside of the leaves, spots may appear as a darker green color or “water-soaked.” As the disease progresses, traveling from older growth to younger growth, spots may coalesce and the leaves may become entirely blighted. The fruit is rarely infected by this fungus.

Look alike diseases: It can be difficult to distinguish among numerous fungal, foliar leaf spots on tomato. Keep in mind, multiple fungal diseases may be present on a plant making identification even more challenging. Lesions caused by the early blight pathogen will be larger and darker brown than Septoria leaf spots and will have concentric rings. Gray leaf spot, caused by species of Stemphylium, will be very similar to Septoria leaf spots where they are small, circular, with a tan or light brown center, but the center part of the lesion tends to crack open or fall out in gray leaf spot lesions. Most hybrid varieties have resistance to gray leaf spot, but many or most heirloom tomatoes do not have resistance, so it may be difficult to distinguish Septoria leaf spots from gray leaf spot on these varieties.

Gray leaf spot on tomato foliage

Favorable Environmental Conditions for Disease

Areas with high humidity and warm temperatures are most susceptible to this disease. The fungus is known to overwinter on infected tomato debris and solanaceous weed hosts (such as horsenettle). Once an area has become infected, spores are generally spread by rain splash. Water is needed to spread the spores and even workers, equipment, or insects travelling through wet foliage infected with Septoria leaf spot can aid in the spreading of the disease.

Disease Control for Conventional Growers

In addition to the cultural practices listed above, there are several products that are effective at controlling the disease. For the latest fungicide recommendations for Septoria leaf spot, consult the Southeastern US Vegetable Crop Handbook.

Example products for control of Septoria leaf spot in tomato.

Active Ingredient

Example Product

PHI (days)

FRAC Group

azoxystrobin

Quadris

0

11

chlorothalonil

Bravo

0

M

chlorothalonil + cymoxanil

Ariston

3

M + 27

difenoconazole +cyprodinil

Inspire Super

0

3 + 9

penthiopyrad

Fontelis

0

7

famoxadone + cymoxanil

Tanos

3

11 + 27

fluopyram + trifloxystrobin

Luna Sensation

3

7 + 11

fluxapyroxad + pyraclostrobin

Priaxor

7

7 + 11

fixed copper

Kocide

0

M

mancozeb

Penncozeb

5

M

mancozeb + fixed copper

ManKocide

7

M + M

mancozeb + zoxamide

Gavel

5

M + 22

mandipropamid + difenoconazole

Revus Top

1

40 + 3

penthiopyrad

Fontelis

0

7

zinc dimethyldithiocarbamate

Ziram

7

M

Disease Control for Organic Growers

There are limited products available for controlling Septoria leaf spot on tomato. Organic fungicides have limited efficacy, so it is important to implement cultural practices before considering organic fungicides. Some formulations of copper are certified for organic use and may provide adequate control. Be sure to follow directions on the product label.

For gardens with a history of Septoria leaf spot, fungicides with active ingredients such as chlorothalonil, copper, or mancozeb will help reduce disease, but they must be applied before disease occurs as they can only provide preventative protection. They will not cure the plant.

Related Publications

The use of brand names in this publication does not imply endorsement by NC State University or N.C. A&T State University of the products or services named nor discrimination against similar products or services not mentioned.

Recommendations for the use of agricultural chemicals are included in this publication as a convenience to the reader. The use of brand names and any mention or listing of commercial products or services in this publication does not imply endorsement by NC State University or N.C. A&T State University nor discrimination against similar products or services not mentioned. Individuals who use agricultural chemicals are responsible for ensuring that the intended use complies with current regulations and conforms to the product label. Be sure to obtain current information about usage regulations and examine a current product label before applying any chemical. For assistance, contact your local N.C. Cooperative Extension county center.

North Carolina State University and North Carolina A&T State University commit themselves to positive action to secure equal opportunity regardless of race, color, creed, national origin, religion, sex, age, veteran status or disability. In addition, the two Universities welcome all persons without regard to sexual orientation.